This invention relates to joining elongated members such as elements of guidewires for advancing intraluminal devices within body lumens. Conventional guidewires for stent delivery catheters, balloon dilatation catheters, atherectomy catheters and the like usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil disposed about the distal portion of the core member. A shapeable member, which may be the distal extremity of the core member or a separate shaping ribbon which is secured to the distal extremity of the core member extends through the flexible body and is secured to a rounded plug at the distal end of the flexible body. Torquing means are provided on the proximal end of the core member to rotate, and thereby steer, the guidewire while it is being advanced through a patient's vascular system. In some cases, the physician will bend the distal end of the core member to facilitate advancement of, the guidewire through the turns of the patient's body lumen, necessitating the shapeable member.
In a typical coronary procedure, a guiding catheter having a preformed distal tip is percutaneously introduced into a patient's peripheral artery, e.g. femoral or brachial artery, by means of a conventional Seldinger technique and advanced therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. The guidewire is first advanced out of the distal end of the guiding catheter into the patient's coronary vasculature until the distal end of the guidewire crosses a lesion to be dilated. A desired diagnostic or therapeutic system can then be advanced over the guidewire to perform a procedure at the site of the lesion. Typical procedures include balloon angioplasty and intracoronary stent delivery.
A major requirement for guidewires is that they have sufficient column strength to be pushed through a patient's vascular system or other body lumen without kinking. However, the distal portion must also be flexible enough to avoid damaging the blood vessel or other body lumen through which they are advanced. Efforts have been made to improve both the strength and flexibility of guidewires to make them more suitable for their intended uses, but these two properties are for the most part diametrically opposed to one another in that an increase in one usually involves a decrease in the other.
Further details of guidewires, and devices associated therewith for various interventional procedures can be found in U.S. Pat. No. 4,748,986 (Morrison et al.); U.S. Pat. No. 4,538,622 (Samson et al.): U.S. Pat. No. 5,135,503 (Abrams); U.S. Pat. No. 5,341,818 (Abrams et al.); U.S. Pat. No. 5,636,641 (Fariabi); and U.S. Pat. No. 5,345,945 (Hodgson, et al.) which are hereby incorporated herein in their entirety by reference thereto.
One approach to achieving both flexibility and column strength in a guidewire is to use a pseudoelastic alloy for a core member, such as NiTi. When stress is applied to a core member exhibiting pseudoelastic characteristics at a temperature at or above which the transformation of martensite phase to the austenite phase is complete, the core member deforms elastically until it reaches a particular stress level where the alloy then undergoes a stress-induced phase transformation from the austenite phase to the martensite phase. As the phase transformation proceeds, the alloy undergoes significant increases in strain but with little or no corresponding increases in stress. The strain increases while the stress remains essentially constant until the transformation of the austenite phase to the martensite phase is complete. Thereafter, further increase in stress is necessary to cause further deformation.
If the load on the pseudoelastic alloy is removed before any permanent deformation has occurred, the martensitic core metal will elastically recover and transform back to the austenite phase. The reduction in stress first causes a decrease in strain. As stress reduction reaches the level at which the martensite phase transforms back into the austenite phase, the stress level in the specimen will remain essentially constant (but substantially less than the constant stress level at which the austenite transforms to the martensite) until the transformation back to the austenite phase is complete, i.e. there is significant recovery in strain with only negligible corresponding stress reduction. After the transformation back to austenite is complete, further stress reduction results in elastic strain reduction.
This ability to incur significant strain at relatively constant stress upon the application of a load and to recover from the deformation upon the removal of the load is commonly referred to as pseudoelasticity. These properties to a large degree allow a guidewire core of a pseudoelastic material to have both flexibility and strength. However, many pseudoelastic alloys, particularly titanium containing alloys, are difficult to join or secure to other components, primarily because a tenacious oxide layer that develops on the surface of such alloys. Prior methods for attaching subassemblies to psuedoelastic or superelastic components included molten or fusion salt etching and then pre-tinning with gold or similar materials to facilitate forming a strong bond, as seen in U.S. Pat. No. 5,695,111 to Nanis, et al. which is hereby incorporated in its entirety. In addition, it is often desirable for a guidewire to have an integral core member of a unitary piece of metal that extends from a proximal section to the distal tip of the guidewire. However, it also often desirable for the distal tip of a guidewire to be shapeable with manual deformation so that a physician can tailor the shape of the distal tip to the vasculature that must be traversed. As discussed above, pseudoelastic alloys can withstand a large amount of stress without incurring plastic deformation, and are thus difficult to shape when used as core members in distal guidewire sections.
What has been needed and heretofore unavailable, however, is a method for manufacturing a guidewire with a superelastic or pseudoelastic component which will allow the component to accept a weld, solder or adhesive joint with ease of manufacture and low cost. What has also been needed is a distally contiguous distal segment of a guidewire core made of a pseudoelastic or superelastic alloy which can be shaped or bent to allow for guiding, without the need of a separate non-pseudoelastic piece, i.e. a stainless steel shaping ribbon.